Acrylonitrile-butadiene-styrene (ABS) resins are widely used in various applications, for example, automobiles, electrical and electronic devices, office machines, household electric appliances, toys and the like, due to their high impact resistance, good processability, high mechanical strength and attractive appearance.
Generally, processes for producing ABS resins can be broadly classified into the following three groups. The first process is a compounding process in which butadiene as a raw material is emulsion polymerized, styrene and acrylonitrile are added thereto to prepare a graft ABS, and the graft ABS is compounded with a styrene-acrylonitrile (SAN) resin. The second is a bulk suspension process in which butadiene, styrene and acrylonitrile are polymerized to prepare an ABS resin in the form of a bulk polymer and the ABS resin is subjected to suspension polymerization after phase conversion. The third process is a mass/continuous process in which all raw materials are added all together to prepare a final ABS resin at one time.
There are some advantages to the compounding process, such as the use of a relatively small production system. Also, the use of small-sized graft ABS particles produced in batch polymerization can enable the preparation of attractive, high gloss ABS, and the composition of raw materials can be easily changed during compounding to control the physical properties of ABS. However, the final product is produced through many processing steps, which can make it difficult to manage the physical properties of ABS. The addition of additives, such as an emulsifier and a dispersant, during batch polymerization can also cause additional problems.
The bulk-suspension process was mainly employed at the initial stage of ABS development. According to the bulk-suspension process, only one reactor is used for the preparation of an ABS product with relatively stable physical properties. The bulk-suspension process can reduce operation costs and use less energy. However, the bulk-suspension process is very inefficient for large-scale production of ABS. Due to this disadvantage, at present there is only limited investment in ABS mass production equipment for bulk-suspension processing.
The mass/continuous process can allow stable production of large amounts of ABS at one time. The kind of rubbers available for use in mass/continuous processes, however, is limited, and the use of rubbers prepared in other processes can make it difficult to control the inherent physical properties of the rubbers. This in turn can result in many limitations in the production and development of various products.
A conventional ABS production method using the mass/continuous process includes: polymerizing a conjugated diene monomer, stripping the polymerization product to remove solvent and water and preparing the rubber in the form of a bale (first step); pulverizing the rubber bale so as to be suitable for use in a subsequent ABS resin production process and dissolving the rubber pieces in a polymerizable monomer to make a rubber solution (second step); and mixing the rubber solution with a solvent, continuously feeding the mixture into a reactor, polymerizing the mixture, and pelletizing the polymerization product to produce final ABS pellets (third step).
The first step includes the sub-steps of solvent stripping and water removal and preparing a rubber bale. These sub-steps can require a large amount of steam, and thus a large quantity of energy, and can discharge a large amount of wastewater. Another disadvantage is that the rubber pulverization and dissolution can also be energy-consuming. In addition, these steps can increase equipment operation and labor costs.
Thus, there is a need to develop a method for producing a thermoplastic resin by directly adding a rubber solution to a thermoplastic resin polymerization process which can minimize or eliminate the number of post rubber polymerization processes steps, such as forming a rubber bale and pulverizing the rubber.